Capture and process video frames with Phonon

Friðrik Ásmundsson fridrik at
Fri Jun 27 15:49:49 BST 2008


I am coming from the computer vision background and I have been developing a
SIFT fingerprint solution for movies. How this works is that I need to
decode common video formats and get direct access to the pixels in each
frame in the movie. When I have created all the fingerprints from each frame
(there are several hundred), I need to process the next frame, and so on.
The extraction process is quite quick (it is implemented on the GPU) and
takes therefore about 1/5 of realtime playback of the video. What I have
done up to now is that I wrote an MPlayer video-out plugin which writes the
frame pixels to shared memory and pauses the playback until the pixels in
shared memory have been processed (guarded by semaphore), then the next
frame is processed and so on. This works Ok, but I think it is possible to
do this more intelligent.

What I need is a direct access to the pixels from each frame (I don't need
to display the movie on-screen) and having the ability to pause the playback
while the image analysis process is working. If I understand correctly, is
seems that I could implement the image analysis part as an "Effect" entity,
but I am not sure if is possible to pause backend, also is it possible to
play movies at higher speed (5X normal playback)?

Therefore I am asking if Phonon could be used for the scenario I described

Fridrik Heidar Asmundsson
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